3.2. Synthesis of Target Compounds

Formyl hydroxycoumarin 9 (1.0 eq.) was added to a solution of ferrocenyl amine 10a or 10b (1.0 eq.) in ethanol (15 mL) and the resulting mixture was refluxed for 4 h. The reaction mixture was cooled to room temperature following 4 h of reflux and sodium borohydride (2.0 eq.) was cautiously added. The reaction was then stirred at room temperature for 15 min and refluxed for another 15 min after which it was allowed to cool to room temperature. The product was extracted into the aqueous phase with 2N HCl solution (2 × 25 mL) and washed with EtOAc (25 mL). The collected aqueous layers were basified with 1N NaOH solution (pH 10) and the product extracted with DCM (2 × 25 mL), dried (Na₂SO₄) and solvent removed in vacuo to afford the title compound. Column chromatography on basic alumina was employed to purify the compounds where necessary using gradient elution (DCM→1:9 MeOH/DCM).

8-((Ferrocenemethyl)aminomethyl)-7-hydroxycoumarin (11a). Light brown semi-solid. Yield: 235.2 mg (86%). ¹H NMR (600 MHz, DMSO-d₆) δ 7.83–7.81 (m, 2H, H₅, H₇), 7.34 (t, J = 7.4 Hz, 1H, H₆), 7.10–7.03 (m, 2H, H₆, H₈), 4.16 (s, 2H, FcH), 4.13 (s, 2H, FcH), 4.10 (s, 5H, FcH), 4.02 (s, 2H, H_3’), 3.55 (s, 2H, H_1’); ¹³C NMR (150 MHz, DMSO-d₆) δ 173.1, 165.0, 153.9, 129.4, 124.7, 123.6, 121.5, 115.5, 95.1, 88.9, 68.2 (5C), 67.4 (2C), 66.8 (2C), 46.9, 44.2; IR (ATR, cm⁻¹) ν = 3080 (O-H), 2914 (N-H); HRMS (ESI⁺) m/z calcd for C₂₁H₂₀FeNO₃ [M + H]⁺: 390.0793, Found 390.0782; HPLC purity > 99% (t_R = 2.47 min).

8-((N,N-Dimethylamino)methyl)ferrocenemethyl)-7-hydroxycoumarin (11b). Light brown semi-solid. Yield: 121.6 mg (56%). ¹H NMR (600 MHz, CDCl₃) δ 7.59 (d, J = 9.3 Hz, 1H, H₃), 7.23 (d, J = 8.4 Hz, 1H, H₆), 6.72 (d, J = 8.4 Hz, 1H, H₅), 6.10 (d, J = 9.3 Hz, 1H, H₄), 4.22 (br s, 1H, FcH), 4.18 (br s, 1H, FcH), 4.13–4.12 (m, 2H, H_8’), 4.09 (br s, 1H, FcH), 4.04 (s, 5H, FcH), 3.91 (d, J = 13.2 Hz, 1H, H_2’a), 3.79 (d, J = 12.7 Hz, 1H, H_1’a), 3.42 (d, J = 13.2 Hz, 1H, H_2’b), 2.80 (d, J = 12.6 Hz, 1H, H_1’b), 2.15 (s, 6H, NMe₂); ¹³C NMR (150 MHz, CDCl₃) δ 161.9, 153.6, 144.7, 128.1, 115.1, 110.2, 110.1, 107.4, 100.1, 84.2, 82.6, 69.9, 69.5, 69.2 (5C), 69.0, 58.4, 46.4, 44.9 (2C), 44.6; IR (ATR, cm⁻¹) ν = 3085 (O-H), 2918 (N-H); HRMS (ESI⁺) m/z calcd for C₂₄H₂₇FeN₂O₃ [M + H]⁺: 447.1371, Found 447.1371; HPLC purity > 99% (t_R = 2.46 min).

CDI (1.2 eq.) was added to a solution of a relevant acyclic ferrocenyl aminohydroxycoumarin (11a or 11b) (1.0 eq.) in DCM (15 mL). The resultant reaction mixture was stirred at room temperature for 1–2 h. After completion of the reaction (TLC), unreacted CDI was quenched by the addition of 0.5N NaOH solution (15 mL) and the product extracted with DCM (2 × 25 mL). The combined organic layers were washed with distilled water (25 mL), dried (Na₂SO₄) and the solvent was removed under reduced pressure to furnish the desired carbamate products 12a,b in high purity.

9-Ferrocenemethyl-9,10-dihydro-2H,8H-chromeno[8,7-e][1,3]oxazine-2,8-dione (12a). Light brown semi-solid. Yield: 146.0 mg (96%). M.p.: 145.4–148.0 °C. ¹H NMR (400 MHz, DMSO-d₆/Acetone-d₆) δ 8.03 (d, J = 9.3 Hz, 1H, H₃), 7.66 (d, J = 8.4 Hz, 1H, H₆), 7.01 (d, J = 8.2 Hz, 1H, H₅), 6.41 (d, J = 9.4 Hz, 1H, H₄), 4.57 (s, 2H, H₁₀), 4.47 (s, 2H, H_1’), 4.40 (s, 2H, FcH), 4.23 (s, 5H, FcH), 4.19 (s, 2H, FcH); ¹³C NMR (100 MHz, DMSO-d₆/Acetone-d₆) δ 159.3, 151.6, 150.1, 148.2, 144.1, 128.7, 114.8, 114.2, 112.0, 105.8, 81.4, 69.4, 68.5, 68.2, 47.9, 42.0; IR (ATR, cm⁻¹) ν = 1716 (C=O); HRMS (ESI⁺) m/z calcd for C₂₁H₂₀FeNO₃ [M − CO + H₃]⁺: 390.0787, Found 390.0781; HPLC purity > 99% (t_R = 2.50 min).

9-(2-((N,N-Dimethylamino)methyl)ferrocenemethyl)-9,10-dihydro-2H,8H-chromeno[8,7-e][1,3]oxazine-2,8-dione (12b). Light yellow solid. Yield: 62.2 mg (90%). M.p.: 105.3–108.6 °C. ¹H NMR (400 MHz, CDCl₃) δ 7.63 (d, J = 9.6 Hz, 1H, H₃), 7.34 (d, J = 8.5 Hz, 1H, H₆), 6.91 (d, J = 8.5 Hz, 1H, H₅), 6.31 (d, J = 9.6 Hz, 1H, H₄), 4.73–4.68 (m, 2H, H₁₀), 4.55–4.48 (m, 2H, H_2’), 4.39 (br s, 1H, FcH), 4.29 (br s, 1H, FcH), 4.16 (t, J = 2.4 Hz, 1H, FcH), 4.13 (s, 5H, FcH), 3.83–3.70 (m, 1H, H_1’a), 3.15–3.03 (m, 1H, H_1’b), 2.19 (s, 6H, NMe₂); ¹³C NMR (100 MHz, CDCl₃) δ 160.0, 152.3, 150.5, 149.4, 143.3, 127.9, 114.9, 114.8, 112.7, 106.5, 80.9 (2C), 71.9, 71.2, 69.5 (5C), 67.8, 57.2, 46.9, 44.4 (2C), 41.9; IR (ATR, cm⁻¹) ν = 1720 (C=O); HRMS (ESI⁺) m/z calcd for C₂₄H₂₅FeN₂O₄ [M + H]⁺: 473.1164, Found 473.1159;); HPLC purity > 99% (t_R = 3.43 min).

Aminohydroxycoumarin 11b (1.0 eq.) in CHCl₃ (20 mL) was refluxed with paraformaldehyde (1.0 eq.) for 12 h, after which the reaction was cooled to room temperature. The reaction mixture was diluted with CHCl₃ (50 mL) and successively washed with 1N NaOH solution (2 × 25 mL) and distilled water (25 mL). The organic layer was dried (Na₂SO₄) and the solvent removed in vacuo to afford the target compound in high purity as a light yellow semi-solid. Yield: 94.3 mg (68%). ¹H NMR (600 MHz, CDCl₃) δ 7.62 (d, J = 9.4 Hz, 1H, H₃), 7.24 (s, 1H, H₆), 6.76 (d, J = 8.5 Hz, 1H, H₅), 6.22 (d, J = 9.4 Hz, 1H, H₄), 4.96 (s, 2H, H₈), 4.26 (br s, 1H, H, H_10a), 4.22–4.21 (m, 2H, FcH, H_8b), 4.12 (t, J = 2.5 Hz, 1H, FcH), 4.06 (s, 1H, FcH), 4.01 (s, 5H, FcH), 3.77 (d, J = 13.3 Hz, 1H, H_2’a), 3.73 (d, J = 13.3 Hz, 1H, H_2’b), 3.31–3.27 (m, 1H, H_1’a), 3.10 (d, J = 12.9 Hz, 1H, H_2’b), 2.07 (s, 6H, NMe₂); ¹³C NMR (150 MHz, CDCl₃) δ 161.3, 158.0, 152.8, 144.1, 126.5, 113.7, 112.6, 112.2, 108.7, 84.4, 83.3, 82.9, 70.8, 70.3, 69.4 (5C), 67.4, 57.5, 49.8, 45.3 (2C), 44.6; IR (ATR, cm⁻¹) ν = 1238 (C-O), 1116 (C-N); HRMS (ESI⁺) m/z calcd for C₂₅H₂₇FeN₂O₃ [M + H]⁺: 459.1366, Found 459.1363; HPLC purity > 99% (t_R = 3.40 min).

Compounds 15a–d were prepared from substituted 3-formyl-4-hydroxycoumarins 14a–c and ferrocenyl amines 10a,b following the reaction conditions described for synthesis acyclic derivatives 11a,b.

3-((Ferrocenemethyl)aminomethyl)-coumarin-4-ol (15a). Light brown semi-solid: 235.2 mg (86%). ¹H NMR (600 MHz, DMSO-d₆) δ 7.83–7.81 (m, 2H, H₅, H₇), 7.34 (t, J = 7.4 Hz, 1H, H₆), 7.10–7.03 (m, 2H, H₅, H₈), 4.16 (s, 2H, FcH), 4.13 (s, 2H, FcH), 4.10 (s, 5H, FcH), 4.02 (s, 2H, H_1’), 3.55 (s, 2H, H_1’); ¹³C NMR (150 MHz, DMSO-d₆) δ 173.1, 165.0, 153.9, 129.4, 124.7, 123.6, 121.5, 115.5, 95.1, 88.9, 68.2 (5C), 67.4 (2C), 66.8 (2C), 46.9, 44.2; IR (ATR, cm⁻¹) ν = 3083 (O-H), 2915 (N-H); HRMS (ESI⁺) m/z calcd for C₂₁H₂₀FeNO₃ [M + H]⁺: 390.0793, Found 390.0779; HPLC purity > 91% (t_R = 2.47 min).

3-((2-((N,N-Dimethylamino)methyl)ferrocenemethyl)aminomethyl)-coumarin-4-ol (15b). Brown semi-solid: 350.2 mg (68%). ¹H NMR (600 MHz, CDCl₃ δ 7.83 (dd, J = 7.7, 1.1 Hz, 1H, H₅), 7.40 (td, J = 7.7, 1.4 Hz, 1H, H₇), 7.17 (d, J = 7.8 Hz, 1H, H₈), 7.14 (t, J = 7.5 Hz, 1H, H₆), 4.34 (s, 1H, FcH), 4.19 (br s, 1H, FcH), 4.20–4.17 (m, 2H, H_3’a, FcH), 4.13 (t, J = 2.4 Hz, 1H, FcH), 4.11 (s, 5H, FcH), 4.09 (d, J = 8.8 Hz, 2H, H_2’), 3.90–3.89 (m, 2H, H_1’a, H_3’b), 2.88 (d, J = 13.0 Hz, 1H, H_1’b), 2.16 (s, 6H, NMe₂); ¹³C NMR (150 MHz, CDCl₃) δ 176.1, 165.8, 154.4, 131.1, 124.5, 122.8, 122.0, 116.6, 100.1, 88.8, 84.1, 72.0 (2C), 69.7 (5C), 67.3, 58.1, 45.7, 44.2, 43.7 (2C); IR (ATR, cm⁻¹) ν = 2820 (O-H), 2774 (N-H); HRMS (ESI⁺) m/z calcd for C₂₄H₂₇FeN₂O₃ [M + H]⁺: 447.1371, Found 447.1371; HPLC purity > 96% (t_R = 2.46 min).

3-((2-((N,N-Dimethylamino)methyl)ferrocenemethyl)aminomethyl)-6-fluoro-4-hydroxycoumarin (15c). Light brown semi-solid. 109.0 mg (64%). ¹H NMR (600 MHz, CDCl₃) δ 7.48 (dd, J = 8.6, 2.9 Hz, 1H, H₅), 7.14–7.09 (m, 2H, H₇, H₈), 4.33 (br s, 1H, FcH), 4.20 (br s, 1H, FcH), 4.18 (d, J = 13.4 Hz, 1H, H_2’a), 4.13 (t, J = 2.4 Hz, 1H, FcH), 4.11 (s, 5H, FcH), 4.07 (d, J = 13.0 Hz, 2H, H_3’), 3.87 (d, J = 13.1 Hz, 2H, H_1’a, H_2’b), 2.89 (d, J = 13.0 Hz, 1H, H_1’b), 2.16 (s, 6H, NMe₂); ¹³C NMR (150 MHz, CDCl₃) δ 174.9, 165.8, 159.3, 157.7, 150.3, 123.2 (d, J = 7.9 Hz), 118.3 (d, J = 24.8 Hz), 118.0 (d, J = 7.9 Hz), 109.9 (d, J = 23.8 Hz), 89.2, 84.1, 72.0, 71.9, 69.6 (5C), 67.3, 58.1, 46.0, 44.2 (2C), 43.5; IR (ATR, cm⁻¹) ν = 3076 (O-H), 2915 (N-H); HRMS (ESI⁺) m/z calcd for C₂₄H₂₆FFeN₂O₃ [M + H]⁺: 465.1279, Found 465.1279; HPLC purity > 99% (t_R = 2.48 min).

3-((2-((N,N-Dimethylamino)methyl)ferrocenemethyl)aminomethyl)-6-chloro-4-hydroxycoumarin (15d). Light brown semi-solid. Yield: 174.4 mg (66%). ¹H NMR (600 MHz, CDCl₃) δ 7.75 (d, J = 2.5 Hz, 1H, H₅), 7.31 (dd, J = 8.7, 2.6 Hz, 1H, H₇), 7.09 (d, J = 8.7 Hz, 1H, H₄), 4.31 (br s, 1H, FcH), 4.21 (d, J = 13.3 Hz, 1H_3’a), 4.19 (br s, 1H, FcH), 4.11 (d, J = 4.7 Hz, 6H, FcH), 4.06–4.01 (m, 2H, H_2’), 3.88 (d, J = 13.0 Hz, 1H, H_1’a), 3.85 (d, J = 13.3 Hz, 1H, H_3’b), 2.87 (d, J = 13.0 Hz, 1H, H_1’b), 2.15 (s, 6H, NMe₂); ¹³C NMR (150 MHz, CDCl₃) δ 174.6, 165.5, 152.7, 130.9, 128.2, 124.2, 123.4, 118.1, 100.1, 89.4, 84.1, 72.0, 71.9, 69.6 (5C), 67.3, 58.1, 46.0, 44.2 (2C), 43.3; IR (ATR, cm⁻¹) ν = 3070 (O-H), 2923 (N-H); HRMS (ESI⁺) m/z calcd for C₂₄H₂₆ClFeN₂O₃ [M + H]⁺: 481.0976, Found 481.1568; HPLC purity > 99% (t_R = 2.47 min).

Compounds 16a–d were synthesized according to the general procedure employed for the synthesis of coumarin-1,3-oxazin-2-one derivatives 12a,b from aminocoumarin-4-ols 15a–d.

3-Ferrocenemethyl-3,4-dihydro-2H,5H-chromeno[3,4-e][1,3]oxazine-2,5-dione (16a). Light brown semi-solid. Yield: 41.0 mg (68%). ¹H NMR (600 MHz, CDCl₃) δ 7.78 (dd, J = 8.1, 1.4 Hz, 1H, H₇), 7.51 (td, J = 8.4, 1.4 Hz, 1H, H₈), 7.35–7.33 (m, 2H, H₉, H₁₀), 4.40 (s, 2H, H₄), 4.26 (br s, 2H, FcH), 4.12 (br s, 9H, FcH, H_1’); ¹³C NMR (150 MHz, CDCl₃) δ 159.8, 155.9, 153.2, 147.1, 133.1, 124.9, 122.8, 117.0, 113.0, 98.2, 80.1, 70.0 (2C), 69.2 (2C), 68.9 (5C), 49.3, 43.3; IR (ATR, cm⁻¹) ν = 1738 (C=O); HRMS (ESI⁺) m/z calcd for C₂₂H₁₈FeNO₄ [M + H]⁺: 416.0586, Found 416.0586; HPLC purity > 98% (t_R = 3.03 min).

3-(2-((N,N-Dimethylamino)methyl)ferrocenemethyl)-3,4-dihydro-2H,5H-chromeno[3,4-e][1,3]oxazine-2,5-dione (16b). Light brown semi-solid. Yield: 37.3 mg (75%). ¹H NMR (600 MHz, CDCl₃) δ 7.88 (d, J = 7.8 Hz, 1H, H₇), 7.58 (t, J = 7.6 Hz, 1H, H₈), 7.33–7.33 (m, 2H, H₉, H₁₀), 4.81 (d, J = 14.5 Hz, 1H, H_4a), 4.38 (d, J = 14.5 Hz, 1H, H_4b), 4.33–4.31 (m, 2H, H_2’a, FcH), 4.28 (s, 1H, FcH), 4.21 (br s, 1H, FcH), 4.14–4.13 (m, 6H, H_2’b, FcH), 3.66 (d, J = 12.4 Hz, 1H, H_1’a), 2.90 (br s, 1H, H_1’b), 2.10 (s, 6H, NMe₂); ¹³C NMR (150 MHz, CDCl₃) δ 159.8, 155.6, 153.2, 147.6, 132.8, 124.8, 122.7, 117.0, 113.1, 98.8, 88.5, 80.5, 72.0, 71.3, 69.5 (5C), 67.5, 57.5, 47.2 (2C), 44.9, 42.5; IR (ATR, cm⁻¹) ν = 1752 (C=O); HRMS (ESI⁺) m/z calcd for C₂₄H₂₇ClFeN₂O₃Na [M − CO + NaCl + H₃]⁺: 505.0952, Found 505.1424; HPLC purity > 91% (t_R = 2.43 min).

3-(2-((N,N-Dimethylamino)methyl)ferrocenemethyl)-9-fluoro-3,4-dihydro-2H,5H-chromeno[3,4-e][1,3]oxazine-2,5-dione (16c). Light brown semi-solid. Yield: 16.6 mg (36%). ¹H NMR (600 MHz, CDCl₃) δ 7.56 (dd, J = 8.0, 2.8 Hz, 1H, H₁₀), 7.33–729 (m, 2H, H₇, H₁₈), 4.79 (d, J = 14.5 Hz, 1H, H_4a), 4.39 (d, J = 14.5 Hz, 1H, H_4b), 4.34–4.29 (m, 2H, H_2’a, FcH), 4.18 (s, 1H, FcH), 4.15–4.09 (m, 7H, H_2’b, FcH), 3.64 (d, J = 12.6 Hz, 1H, H_1’a), 2.84 (d, J = 12.6 Hz, 1H, H_1’b), 2.07 (s, 6H); ¹³C NMR (150 MHz, CDCl₃) δ 159.5, 158.2, 154.8, 149.3, 147.2, 120.4 (d, J = 24.6 Hz), 118.7 (d, J = 8.3 Hz), 114.1, 108.6 (d, J = 25.9 Hz), 99.8, 84.9, 80.3, 72.1, 71.3, 69.5 (5C), 67.4, 57.6, 47.3, 45.0 (2C), 42.5; IR (ATR, cm⁻¹) ν = 1717 (C=O); HRMS (ESI⁺) m/z calcd for C₂₄H₂₆ClFFeN₂O₃Na [M − CO + NaCl + H₃]⁺: 523.1338, Found 523.1338; HPLC purity > 91% (t_R = 2.60 min).

3-(2-((N,N-Dimethylamino)methyl)ferrocenemethyl)-9-chloro-3,4-dihydro-2H,5H-chromeno[3,4-e][1,3]oxazine-2,5-dione (16d). Light brown semi-solid. Yield: 17.3 mg (49%). ¹H NMR (600 MHz, CDCl₃) δ 8.06 (d, J = 2.4 Hz, 1H, H₁₀), 7.71 (dd, J = 8.8, 2.4 Hz, 1H, H₈), 7.47 (d, J = 8.9 Hz, 1H, H₇), 4.98 (d, J = 14.5 Hz, 1H, H_4a), 4.59 (d, J = 14.5 Hz, 1H, H_4b), 4.51–4.49 (m, 2H, FcH, H_2’a), 4.38 (br s, 1H, FcH), 4.33–4.32 (m, 7H, FcH, H_2’b), 3.83 (d, J = 12.5 Hz, 1H, H_1’a), 3.03 (d, J = 12.6 Hz, 1H, H_1’b), 2.27 (s, 6H, NMe₂); ¹³C NMR (150 MHz, CDCl₃) δ 159.2, 154.5, 151.4, 147.1, 132.9, 130.5, 122.3, 118.4, 114.2, 99.8, 84.9, 80.3, 72.1, 71.3, 69.5 (5C), 67.4, 57.6, 47.2, 45.0 (2C), 42.4; IR (ATR, cm⁻¹) ν = 1717 (C=O); HRMS (ESI⁺) m/z calcd for C₂₄H₂₆Cl₂FeN₂O₃Na [M − CO + NaCl + H₃]⁺: 539.1057, Found 539.1057; HPLC purity > 99% (t_R = 2.58 min).

Compound 19 was synthesized from sesamol 18 (1.0 eq) and paraformaldehyde (2.0 eq.) following the procedure described for the synthesis of coumarin-oxazine 13. Brown semi-solid. Yield: 135.5 mg (85%). ¹H NMR (400 MHz, CDCl₃) δ 6.39 (s, 1H, H₉), 6.38 (s, 1H, H₄), 5.87 (s, 2H, H₂), 4.85–4.77 (m, 2H, H₆), 4.25 (br s, 1H, FcH), 4.22 (br s, 1H, FcH), 4.12–4.11 (m, 1H, FcH), 4.02 (s, 5H, FcH), 3.93 (br s, 2H, H₈), 3.73 (s, 2H, H_2’), 3.30 (d, J = 12.9 Hz, 1H, H_1’a), 3.19 (d, J = 12.9 Hz, 1H, H_1’b), 2.16 (s, 6H, NMe₂); ¹³C NMR (100 MHz, CDCl₃) δ 148.8, 146.6, 141.5, 111.7, 106.9, 100.8, 98.5, 84.2, 83.9, 82.4, 70.7, 70.3, 69.4 (5C), 67.2, 57.4, 49.3, 49.3, 45.4 (2C); IR (ATR, cm⁻¹) ν = 1241 (C-O), 1141 (C-N), HRMS (ESI⁺) m/z calcd for C₂₃H₂₇FeN₂O₃ [M + H]⁺: 435.1366, Found 435.1370; HPLC purity > 99% (t_R = 2.40 min).